In inkjet printing systems, it is desirable to have several characteristics of each print cartridge easily identifiable by a controller, and it is desirable to have such identification information supplied directly by the print cartridge. The “identification information”, for example, can provide information to the printer controller to adjust the operation of the printer and ensure correct operation. A print cartridge can store this identification information using a small, non-volatile memory, such as an erasable programmable read-only memory (EPROM).
EPROMs can include a conductive grid of columns and rows. The cell at each intersection can have two gates that are separated from each other by an oxide layer that acts as a dielectric. One of the gates is called a “floating gate” and the other is called a control gate or input gate. The floating gate's only link to the row is through the control gate. A blank EPROM has all of the gates fully open, giving each cell a value of logic ‘0’ (low resistance state). That is, the floating gate initially has no charge, which causes the threshold voltage to be low.
To change the value of the bit to logic ‘1’ (high resistance state), a programming voltage is applied to the control gate and drain. The programming voltage draws excited electrons to the floating gate, thereby increasing the threshold voltage. The excited electrons are pushed through and trapped on the other side of the thin oxide layer, giving it a negative charge. These negatively charged electrons act as a barrier between the control gate and the floating gate. During use of the EPROM cell, a cell sensor can monitor the threshold voltage of the cell. If the threshold voltage is low (below the threshold level), the cell has a value of logic ‘0’. If the threshold voltage is high (above the threshold level), the cell as a value of logic ‘1’.